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Abstract

Apparatus and methods for improving signal detection and tracking in underwater acoustic devices receiving a set of acoustic pulses propagated in response to repetitive synchronizing events. Each of the set of pulses is correlated with a replica of each pulse in a receiver in the underwater devices during an associated time window. The correlated output of the receiver is compared to an adjustable threshold characteristic in a detector for selection of the actual pulse according to predetermined criteria for each of the set of pulses. An actual time of reception relative to the synchronizing event is assigned to the selected pulse. Previous actual times of reception are used to estimate the expected time of reception of the associated pulse relative to the next synchronizing event. The estimate is used to adjust the associated time window to encompass the expected time of reception. Previous actual times of reception are compared to corresponding estimated times of reception to develop a measure of the quality of the estimates. The shape of the threshold characteristic and the width of the associated time window are adjusted as a function of the measure of the quality. A preferred threshold characteristic has a parabolic shape with its vertex defining a minimum threshold level at the expected time of reception. High quality measures lower the minimum threshold and narrow the parabola and the time window; low quality measures raise the minimum threshold level and broaden the parabola and the time window. Adaptive signal tracking is thereby provided.

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